In the environment of a nuclear reactor such as a boiling water reactor (BWR) for example, components within the reactor pressure vessel are located at a substantial distance below the top thereof and underwater when flooded during maintenance operations. Reactor components are typically assembled and disassembled by remote manipulation through the water to provide maximum shielding and distance from the radioactive environment adjacent the nuclear reactor core.
Threaded fasteners such as bolts and nuts are often used for assembling together components within the reactor. The engagement thereof is relatively difficult since limited access is typically provided in the crowded reactor pressure vessel and due to the flexibility of the remote handling tools which may extend up to about 25 meters below the operator and through the water.
A typical conventional bolt has a thread with a blunt or tapered start or leading edge for engaging with the respective leading edge or start end of the nut. The nut and bolt must be suitably initially axially aligned with each other with the respective threads being disposed closely adjacent to each other within a relatively small percentage of the thread pitch, for example about 5%, to ensure effective mating of the threads as they are rotated into engagement. Other configurations of the bolt front end are also conventionally known for more accurately initially joining together the bolt to the nut without damaging the threads due to misalignment or cross-threading thereof. However, conventional configurations vary in effectiveness and vary in their ability to be assembled using remote robotic or manipulation devices such as those required in the environment of the BWR for engagement at a substantial distance underwater.